In Drosophila melanogaster the fruitless (fru) gene is at the top of a branch of the sex determination hierarchy that functions in a small part of the central nervous system (CNS) to control all aspects of male courtship behavior. Fru, like other genes in the sex determination hierarchy, is sex-specifically regulated at the level of differential RNA splicing. The goal of the proposed research is to understand how male-specific FRU, which is a transcription factor, creates the potential for male-courtship behavior. The specific aim of the proposed research is the identification and characterization of male-specific FRU target genes from two developmental stages when male-specific FRU is expressed. The proposed research will proceed as follows. PolyA mRNA from heads of males, females and fru mutant males will be isolated and used as a template to make fluorescently labeled probes. A Drosophila EST cDNA microarray will be probed with two-color fluorescently labeled probes to identify genes that are more highly expressed in male brains as compared to female brains, and that required male-specific FRU for this higher expression. Alternative sources of probes are also presented in case a sufficient number of target genes are not identified. Potential male-specific FRU target genes will be analyzed to determine if they are genetically downstream of fru and to determine their genetic function in creating the potential for male courtship behavior.